Magnetic core, coil component and magnetic core manufacturing method

Abstract

A magnetic core includes alloy phases 20 each made of Fe-based soft magnetic alloy grains including M1 (wherein M1 represents both elements of Al and Cr), Si, and R (wherein R represents at least one element selected from the group consisting of Y, Zr, Nb, La, Hf and Ta), and has a structure in which the alloy phases 20 are connected to each other through a grain boundary phase 30. In the grain boundary phase 30, an oxide region is produced. The oxide region includes Fe, M1, Si and R and further includes Al in a larger proportion by mass than the alloy phases 20.

The invention claimed is: 
     
       1. A magnetic core, which comprises alloy phases each comprising Fe-based soft magnetic alloy grains comprising M1 (wherein M1 represents both elements of Al and Cr), Si, and R (wherein R represents at least one element selected from the group consisting of Y, Zr, Nb, La, Hf and Ta), and which has a structure in which the alloy phases are connected to each other through a grain boundary phase formed by oxidizing the Fe-based soft magnetic alloy grains, wherein in an observation image of a cross section of the magnetic core through SEM at a magnifying power of 1,000, an abundance ratio of alloy phases having a maximum diameter of 40 μm or more is 1% or less,
 wherein the grain boundary phase comprises an oxide region comprising Fe, M1, Si and R and further comprising Al in a larger proportion by mass than the alloy phases, and 
 the oxide region includes a region having a higher proportion of the quantity of R than a region which is different from the higher-R-proportion region and is inside the oxide region. 
 
     
     
       2. The magnetic core according to  claim 1 , wherein a content of Al is 3 to 10% by mass, a content of Cr is 3 to 10% by mass, a content of R is 0.01 to 1% by mass, considering that the sum of the quantities of Fe, M1 and R is regarded as being 100% by mass. 
     
     
       3. The magnetic core according to  claim 2 , comprising R in a proportion of 0.3% or more by mass. 
     
     
       4. The magnetic core according to  claim 2 , comprising R in a proportion of 0.6% or less by mass. 
     
     
       5. The magnetic core according to  claim 1 , wherein R represents Zr or Hf. 
     
     
       6. The magnetic core according to  claim 1 , wherein the grain boundary phase has: a first region where the ratio of the quantity of Al to the sum of the quantities of Fe, M1, Si and R is higher than the ratio of the quantity of each of Fe, Cr, Si and R thereto; and a second region where the ratio of the quantity of Fe to the sum of the quantities of Fe, M1, Si and R is higher than the ratio of the quantity of each of M1, Si and R thereto. 
     
     
       7. The magnetic core according to  claim 1 , having a specific resistance of 1×10 5  Ω·m or more, and a radial crushing strength of 120 MPa or more. 
     
     
       8. A coil component, comprising the magnetic core recited in  claim 1 , and a coil fitted to the magnetic core. 
     
     
       9. A magnetic core, which comprises alloy phases each comprising Fe-based soft magnetic alloy grains comprising M2 (wherein M2 represents either Al or Cr), Si, and R (wherein R represents at least one element selected from the group consisting of Y, Zr, Nb, La, Hf and Ta), and which has a structure in which the alloy phases are connected to each other through a grain boundary phase formed by oxidizing the Fe-based soft magnetic alloy grains, wherein in an observation image of a cross section of the magnetic core through SEM at a magnifying power of 1,000, an abundance ratio of alloy phases having a maximum diameter of 40 μm or more is 1% or less,
 wherein the grain boundary phase comprises an oxide region comprising Fe, M2, Si and R and further comprising M2 in a larger proportion by mass than the alloy phases, and 
 the oxide region includes a region having a higher proportion of the quantity of R than a region which is different from the higher-R-proportion region and is inside the oxide region. 
 
     
     
       10. The magnetic core according to  claim 9 , wherein R represents Zr or Hf. 
     
     
       11. A coil component, comprising the magnetic core recited in  claim 9 , and a coil fitted to the magnetic core. 
     
     
       12. The magnetic core according to  claim 9 , comprising M2 in a proportion of 1.5 to 8% both inclusive by mass, Si in a proportion more than 1% by mass and 7% or less by mass, and R in a proportion of 0.01 to 3% both inclusive by mass provided that the sum of the quantities of Fe, M2, Si and R is regarded as being 100% by mass; and comprising Fe and inevitable impurities as the balance of the core. 
     
     
       13. The magnetic core according to  claim 12 , comprising R in a proportion of 0.3% or more by mass. 
     
     
       14. The magnetic core according to  claim 12 , comprising R in a proportion of 0.6% or less by mass. 
     
     
       15. A magnetic core manufacturing method, comprising the steps of:
 mixing a binder with Fe-based soft magnetic alloy grains comprising M1 (wherein M1 represents both elements of Al and Cr), Si, and R (wherein R represents at least one element selected from the group consisting of Y, Zr, Nb, La, Hf and Ta) to yield a mixed powder; 
 subjecting the mixed powder to pressing to yield a compact; and 
 subjecting the compact to heat treatment in an atmosphere comprising oxygen to yield a magnetic core having a structure comprising alloy phases comprising the Fe-based soft magnetic alloy grains; 
 wherein the heat treatment results in: forming a grain boundary phase through which the alloy phases are connected to each other; and further producing, in the grain boundary phase, an oxide region comprising Fe, M1, Si and R and further comprising Al in a larger proportion by mass than the alloy phases, wherein the magnetic core comprises alloy phases each comprising Fe-based soft magnetic alloy grains comprising M1 (wherein M1 represents both elements of Al and Cr), Si, and R (wherein R represents at least one element selected form the group consisting of Y, Zr, Nb, La, Hf and Ta), and has a structure in which the alloy phases are connected to each other through a grain boundary phase formed by oxidizing the Fe-based soft magnetic alloy grains, 
 wherein in an observation image of a cross section of the magnetic core through SEM at a magnifying power of 1,000, an abundance ratio of alloy phases having a maximum diameter of 40 μm or more is 1% or less, 
 wherein the grain boundary phase comprises an oxide region comprising Fe, M1, Si and R and further comprising Al in a larger proportion by mass than the alloy phases, and the oxide region includes a region having a higher proportion of the quantity of R than a region which is different from the higher-R-proportion region and is inside the oxide region. 
 
     
     
       16. A magnetic core manufacturing method, comprising the steps of:
 mixing a binder with Fe-based soft magnetic alloy grains comprising M2 (wherein M2 represents either Al or Cr), Si, and R (wherein R represents at least one element selected from the group consisting of Y, La, Zr, Hf, Nb and Ta) to yield a mixed powder; and 
 subjecting the mixed powder to pressing to yield a compact; 
 subjecting the compact to heat treatment in an atmosphere comprising oxygen to yield a magnetic core having a structure comprising alloy phases comprising the Fe-based soft magnetic alloy grains; 
 wherein the heat treatment results in: forming a grain boundary phase through which the alloy phases are connected to each other; and further producing, in the grain boundary phase, an oxide region comprising Fe, M2, Si and R and further comprising M2 in a larger proportion by mass than the alloy phases, wherein the magnetic core comprises alloy phases each comprising Fe-based soft magnetic alloy grains comprising M2 (wherein M2 represents either Al or Cr), Si, and R (wherein R represents at least one element selected form the group consisting of Y, Zr, Nb, La, Hf and Ta), and has a structure in which the alloy phases are connected to each other through a grain boundary phase formed by oxidizing the Fe-based soft magnetic alloy grains, 
 wherein in an observation image of a cross section of the magnetic core through SEM at a magnifying power of 1,000, an abundance ratio of alloy phases having a maximum diameter of 40 μm or more is 1% or less, 
 wherein the grain boundary phase comprises an oxide region comprising Fe, M2, Si and R and further comprising M2 in a larger proportion by mass than the alloy phases, and the oxide region includes a region having a higher proportion of the quantity of R than a region which is different from the higher-R-proportion region and is inside the oxide region.